L9177 datasheet(34/49 Pages) STMICROELECTRONICS

34 / 49 page

Functional description

L9177

34/49

DocID17617 Rev 1

4.5.4

Low side on/off diagnosis (INJ, RLY's, TACH, O2H)

About low side channels OFF diagnosis, L9177 issues a masking filter Tmask after channel

turning off (falling edge of driving command) to avoid false fault detecting due to output

transition from low to high. Tmask is of 1 ms ±25 % for all channels except for the relays, for

which Tmask is 3.5 ms ±25 %. Once masking time expires a deglitch filter Tdgc_noise of

3.6 μs ±40 % for noise immunity is activated. A fault longer than deglitch time is latched. Off

state diagnostic fault can be overwritten by on state fault. Off state fault does not prevent the

driver to switch on. The latched fault is cleared on request.

During on-phase if an over current fault occurs the drivers enters in current limitation

condition for a digital filtering time Tdgc of 20 μs ±25 %,then it is switched OFF and the fault

is latched. The channel is turned ON again by input command transition. The latched fault is

cleared on request via SPI.

Over current fault has higher priority respect to OFF condition faults.

Figure 22. Low side driver diagnosis time diagram

L9177 Datasheet(PDF) 34 Page - STMicroelectronics